Identification of Sn precipitates in C-Mn steel containing Sn

In most steels, tin (Sn) is a tramp element due to its hot shortness at grain boundaries and the surface, although Sn also has a vital influence on free-cutting steel, electrical sheets, cast iron, and stainless steel. If the problem of hot shortness is solved, scrap recycling will become much easier and Sn can even be used as an important alloying element. As such, it is most important to investigate the forms of Sn precipitation in C-Mn steels at high temperatures. In this study, Fe-5% Sn and Fe-1.5% Sn-0.2% S steels were investigated to clarify the types of Sn precipitates. The morphology, size, and structure of Sn precipitates were characterized by scanning electron microscopy with energy dispersive spectroscopy and transmission electron microscopy. The influence of heat treatment temperature on the type of Sn precipitates was also investigated. The results show that Sn-riched particles precipitate at grain boundaries and in grains in Fe-5% Sn steels, whereas in Fe-1.5% Sn-0.2% S steels, heterogeneous Sn particles precipitate in the size of spherical MnS inclusions with diameters ranging between 2-4 μm. The transmission electron microscopy analysis and heat treatment experimental results show a FeSn₂ structure with a tetragonal system for Sn precipitates in Fe-5% Sn and Fe-1.5% Sn-0.2% S steels.